There is a new sound in the background music of politics. It goes: ping! Day in, day out, whether the issue is David Cameron's latest move or the Liberal Democrat leadership race, my computer pings away like a fruit machine. And each ping brings me the latest thoughts of influential political commentators - people such as Robin Hutchinson, David Williams, Graham Sharpe and Mike Smithson.

It is possible that you may not have heard of these gents. You can scan all the papers you like and you won't find them writing earnest columns from the Westminster lobby. However doggedly you channel-hop, you won't find them standing under umbrellas on Downing Street. For they don't work for the Telegraph or the Observer, or the BBC or Sky. They work for Ladbrokes, William Hill and politicalbetting.com. But their influence is the latest ingredient in the perpetual, accelerating loop of commentary that politicians struggle to break.

"David Miliband is being steadily backed to succeed Labour leader Tony Blair, according to bookmakers Ladbrokes. The local government minister was 12-1 ..." And: "The odds on Simon Hughes becoming the next permanent leader of the Liberal Democrats have been cut again ... Hughes is now 4-5 from 10-11 ..." Or, another example from the tipping site politicalbetting.com, in July: "We said bet on Cameron at 5-1 ... The price has tightened 4-1 but we stick with our view."

Now, you might say, so what, humans are betting animals. Skinny dogs, nervy horses with tiny men on top of them, football teams of every rank, athletes, dice, cards, even the weather ... people will bet on raindrops running down windows and the colour of the next car round a bend, so of course they will bet on political stories. It is completely natural and entirely harmless, a bit of fun.

So it is. Ranking and betting has always gone on at Westminster, if only in the "Bloggins in the cabinet? I'll give you a fiver" bar-talk way. For those of us not very interested in racing or football, political betting looks rather attractive. Certainly, journalists and politicians have become increasingly interested in the main websites. And, as they have done so, the betting has begun to influence the reporting. It's the latest take on "a new opinion poll reveals ..." Now you hear people announce, as if it's proper news, "bookies are already cutting the odds on ..." On political programmes and 24-hour news shows, bookies have popped up for regularly interviews.

The speeded-up news cycle means that the bookie/punter judgments can help move sentiment fast. The brutal reversal of David Davis's position as frontrunner to lagging also-ran after his faltering Tory conference speech was immediately translated into hard numbers by the bookmakers, and reported.

Before Charles Kennedy resigned, Ladbrokes was widely reported to have cut the odds on Menzies Campbell taking over "after a flurry of bets". Ping! Then, after Simon Hughes entered the race last week, Ladbrokes' Robin Hutchinson reported odds shortening on him, adding that: "We have a great deal of respect for the punters who have backed Hughes as many of them have proved in the past that they know what they are talking about. He certainly has the momentum behind him now. In contrast we've not laid a bet on Campbell or Oaten for 48 hours ..." Ping! (Not Ming!)

These judgments are not just a bit of fun; in leadership races, momentum is everything. The question of who wins may not be decided by such stories, but they help. And there is a small, tight, spinning circle of interlocking judgments being made that needs - in the interests of all of us - a bucket of cold water thrown in its general direction.

There is no mystery about why the bookmakers advertise these stories: they get free publicity. Or why political journalists report these stories: bookies are apparently neutral commentators, giving a hard, factual, numerical basis to what would otherwise be vague, subjective judgments. But here is the problem. Where do the punters get their information from and how many of them, really, are there? Either they are watching the news and reading the papers, and picking up the instant "calls" of the same political journalists and replaying back, via the bookies, those judgments. Or, a high proportion of the punters are insiders and somehow involved themselves. If they are outsiders, then the circularity is comic - reporter X says something; the punter bets; the bookie reports the betting; and reporter X is able to reveal apparently independent evidence that his hunch was right. If the punters are insiders, the situation is arguably even worse. My advice to a Lib Dem leadership contender would be to pay lots of friends to go down to William Hill or Ladbrokes, with bundles of fivers. It might well be the cheapest way of shifting opinion and getting elected.

All this is only the latest twist in the self-referential nature of the Westminster hubbub. Somehow, obscurely, "sentiment" changes and hardens, whatever the slimness of the evidence. David Davis's speech at the party conference wasn't that bad; and Menzies Campbell's question last week wasn't that silly - the hooting and thigh-slapping was a playground response to a slight verbal hesitation. A few years ago, before the instant-judgments culture began, that exchange with Tony Blair would have been a marginal moment.

Politicians can do nothing about the betting, (except try to corrupt it), while keeping their focus on the bigger issues. They have to treat these headlines about their popularity as passing squalls. But the commentariat observing them is in a different position. We shouldn't pretend that fallible and arguable judgments can somehow be made more reliable or scientific because they are then filtered through a small group of people interested in making a buck, and repeated with numbers attached.

Mostly, people have learned this lesson about polling, which is analogous. Politics ought to be about argument, debate, complexity. Political problems, certainly, are long-term, such as how we deal with globalisation, how we cope with labour migration and so on. When we are judging a leader or policy, everyone needs some time to ponder, to think twice, to get things in proportion. But the instant betting loop inhibits this; there's something bullying about "Punters in a Menzies Frenzy". A horse wins, and the race is over, and the next bets can be laid. In politics, a great train of consequences may follow. My January resolution is to give up the pings.